Vacuum insulators, vacuum insulation containers, plasma display panels, and so on can demonstrate their performance when their inside is in the high-vacuum state. These types of equipment are called vacuum equipment. If gas exists inside vacuum equipment, pressure inside the vacuum equipment increases, and the performance of the vacuum equipment degrades. Causes of the presence of gas inside the vacuum equipment include gas remaining in the vacuum equipment at manufacturing, and entrance of gas from outside to inside the vacuum equipment over time. To reduce gas inside the vacuum equipment, gas adsorbent is used. The gas adsorbent adsorbs and reduces the gas inside the vacuum equipment. For example, a vacuum insulator can retain the high-vacuum state for a long period by providing the gas adsorbent inside it.
Gas that the gas adsorbent can adsorb (i.e., adsorption target) differs by materials of gas adsorbents. In addition, an amount of gas that the gas adsorbent can adsorb (i.e., adsorbable amount) differs. An adsorption target of the gas adsorbent used for the vacuum insulator is air (i.e., nitrogen and oxygen). Naturally, if this gas adsorbent is left in the air, it absorbs air. In other words, if this gas adsorbent is left in the air, an amount of air that can be adsorbed reduces. This leads to degradation of the adsorption capacity of the gas adsorbent.
PTL 1 discloses a structure that air is not adsorbed even if the gas adsorbent is left in the air. In PTL1, the gas adsorbent (getter) is sealed between two sheets. These two sheets configure a container of the gas adsorbent. Accordingly, this structure prevents the gas adsorbent from adsorbing air even if it is left in the air. The gas adsorbent is disposed in the vacuum equipment together with this container.
The above gas adsorbent is stored inside the container. Therefore, inside of the container must be kept in the vacuum state, or filled with gas that this gas adsorbent does not adsorb.
If the container is in the vacuum state inside, a pressure difference between atmospheric pressure and vacuum is applied to the container. Therefore, if any hole exists in the container, air enters inside the container. If this gas adsorbent is a gas adsorbent used for the vacuum insulator, an adsorption target is air. In this case, the gas adsorbent adsorbs air entering through the hole in the container.
If air entering inside the container is less than the adsorption capacity of the gas adsorbent, the gas adsorbent adsorbs all amount of air that has entered. Accordingly, the vacuum state inside the container can be retained. In this case, the state inside the container does not change regardless of the presence of hole. In other words, although adsorption capacity of the gas adsorbent has reduced due to adsorption of air, it cannot be noticed.
On the other hand, if the container is filled with gas that this gas adsorbent does not adsorb, and a hole exists in the container, the gas enters inside the vacuum insulator. Accordingly, the high-vacuum state cannot be retained inside the vacuum insulator.